Q4Electrical Machines II

The Torque-Speed characteristic of an induction motor dictates its performance. It is heavily influenced by machine parameters:

1. Rotor Resistance ($R_2$): Increasing the rotor resistance (e.g., via slip rings) increases the starting torque. It also shifts the slip at which maximum (pull-out) torque occurs to a higher value (lower speed). Crucially, the actual magnitude of the maximum torque remains unchanged. Higher resistance increases losses and reduces efficiency during normal running.

2. Stator Voltage ($V_1$): Electromagnetic torque is directly proportional to the square of the applied stator voltage ($Tpropto{V}_1^2$). If the supply voltage drops by 10%, the starting and maximum torque will drop by almost 20%, drastically affecting the motor's ability to drive heavy loads.